Field of the Invention
The present invention relates to sensors for chemical species using nanostructured electronic devices, and methods relating to their use and manufacture, and in particular, to devices employing nanotubes as electronic transducers for the detection and measurement of solvated biomolecules or physiologic species, such as blood glucose.
Description of Related Art
A significant percentage of the US population suffers from diabetes (18.2 million or 6.3%). Of the 18.2 million, 13 million have been diagnosed and of the diagnosed fraction 4 million people take insulin daily. This patient group is supported through numerous foundations and professional associations who provide patient care and education.
Sources report the market growth at 15% annually, driven mainly by increased incidence of disease (obesity, diet) and increased daily monitoring by present patients. Insulin is taken to regulate blood glucose level. The amount of insulin taken must be titrated based on food intake, exercise, physical condition of the user plus the current level of glucose. For the 4 million who follow the insulin dosing protocol blood glucose measurements are suggested 4 to 6 times per day. Diabetics who are not insulin dependent check their blood glucose less frequently, typically 1 or two times a day, to adjust oral medications as well as exercise and food intake. It is estimated that this results in about 9-10 billion glucose determinations per year worldwide.
Self-measurement of glucose is common. Measuring one's own glucose level is typically called Self Monitoring of Blood Glucose (SMBG). Most 5MBG readings are done on a sample of capillary blood obtained by a finger prick. The blood is applied to a disposable sensor “strip” typically an electrochemical sensor containing Glucose Oxidase (GOX). The sensor current or voltage is read by a small electrometer referred to as a glucose meter.
An example of a popular glucose meter is shown in FIG. 1A. The strips are contained in a cartridge. The meter automatically pushes the strips out to collect blood. After use the user must manually remove each strip and dispose of it. Most glucose meters are battery driven and have a measurement range of 20-600 mg/dL. Required blood volume varies between 0.3 and 1 uL. Most meters are provided freely to get payback on strip usage. Disposable strips contain the actual glucose sensor. Capillary action is used to move the blood into the area of the sensor.
FIG. 1B shows a wearable glucose sensor. However, there is a need for glucose measurement and monitoring technology which is more convenient, cheaper, and better suited to integration into other systems, such as invasive or implantable diagnostic or therapeutic devices.